Process for the preparation of salts of 1-substituted 2,4-diaminobenzenes

ABSTRACT

The invention relates to a process for the preparation of specific salts of 1-substituted 2,4-diaminobenzenes by catalytic hydrogenation of 1-substituted 2,4-dinitrobenzenes and addition of the reaction product obtained after the hydrogenation and separated from the catalyst to an aqueous solution of an acid.

BACKGROUND OF THE INVENTION

The present invention relates to a process for the preparation of saltsof 1-substituted 2,4-diaminobenzenes by catalytic hydrogenation of thecorresponding 1-substituted 2,4-dinitrobenzenes and conversion of theresulting reaction product, following removal of the catalyst, into thesalt form.

Salts of 1-substituted 2,4-diaminobenzenes are used in many differentareas. Their synthesis is therefore of particular importance.2-(2′,4′-diamino-diaminophenoxy)-ethanol and its salts are used, forexample, according to DE-A-27 58 735 and DE-A-27 37 138, in oxidationdye compositions as the meta-component.

DE-A-27 58 735 describes the preparation of2-(2′,4′-diaminophenoxy)-ethanol by catalytic hydrogenation of2-(2′,4′-dinitrophenoxy)-ethanol. To remove the catalyst, the reactionmixture after the hydrogenation is filtered in the warmed state, and thefiltrate is recovered. To prepare the dihydrochloride salt of2-(2′,4′-diaminophenoxy)-ethanol, an excess of hydrogen chloride gas isthen introduced into the filtrate. However, this method produces a yieldof only 78%. Reworking this process also shows that the product isproduced in a deep violet color and contains considerable amounts ofby-products and decomposition products, which is manifested in a purityof only 86%. Measurement of the degrees of transmission of a 0.1%strength solution of the product in water according to DIN 55945 givesthe results T_(x)=38.6, T_(y)=26.4 and T_(z)=30.9.

Particularly when the salts of the 1-substituted 2,4-diaminobenzenes,such as 2-(2′,4′-diaminophenoxy)-ethanol, are used in the cosmeticssector, e.g., as precursor compounds in the field of hair cosmetics, thepurity of the 1-substituted 2,4-diaminobenzenes is a decisive factor:even slight contamination by foreign substances is problematical formedicinal reasons (e.g., danger of triggering allergies).

The object of the present invention was therefore to provide a processwith which salts of 1-substituted 2,4-diaminobenzenes and in particularof 2-(2′,4′-diaminophenoxy)-ethanol can be obtained with low impuritiesand low undesired discoloration.

DESCRIPTION OF THE INVENTION

The above-mentioned object is achieved by a process for the preparationof salts of 1-substituted 2,4-diaminobenzenes of the formula (I)

wherein each R¹ is a linear or a branched C₁-C₂₀-alkyl group, aC₆-C₁₈-aryl group, a C₂-C₂₀-acyl group, a COOH group, a COOR³ group inwhich R³ is a linear or a branched C₁-C₂₀-alkyl radical, or N(R⁴)₂, inwhich each R⁴ is hydrogen, a linear or a branched C₁-C₂₀-alkyl radicalor a C₂-C₂₀-acyl radical, and n is an integer from 0 to 3,

R² is a radical of the formula (II)

in which each R⁵ is hydrogen or a C₁-C₅-alkyl radical, m is an integerfrom 1 to 12 and p is an integer from 1 to 4, or a radical of theformula (III),

in which r is an integer from 0 to 2 and optionally one or more carbonatoms of the phenyl ring are replaced by N, O or S, and Y^(⊖) is theequivalent amount of a monovalent, divalent, or a trivalent anion.

Generally, the process involves the step of catalytically hydrogenating1-substituted 2,4-dinitrobenzenes of the formula (IV),

in which R¹, n and R² have the meanings given for formula (I), andseparating the reaction product obtained, after the hydrogenation, fromthe catalyst and adding the reaction product to an aqueous solution ofan acid H^(⊕)Y^(⊖), in which Y^(⊖) has the meaning given above. Theprocess according to the invention is characterized in that the productof the formula (I) can be obtained in an excellent yield of at least80%, preferably at least 85%, particularly preferably at least 89%, andalso with a very high purity of up to 98% and an improved color.

In the 1-substituted 2,4-dinitrobenzenes of the formula (IV), each R¹ ispreferably a linear or a branched C₁-C₁₀-alkyl group, a C₆-C₁₂-arylgroup, a C₂-C₆-acyl group or a N(R⁴)₂ group in which each R⁴ ishydrogen, a linear or a branched C₁-C₆-alkyl radical or a C₂-C₆-acylradical. In addition, n is preferably an integer from 0 to 2.

R² is preferably a radical of the formula (II) in which m is an integerfrom 1 to 9, in particular 1, 2 or 3, R⁵ is hydrogen or methyl, and p is1 or 2. Particularly preferably, the radical R² is —[CH₂—CH₂]—,—[CH(CH₃)—CH₂]— or —[CH₂—C(CH₃)₂—CH₂]—, where p is 1.

In addition, R² is preferably a radical of the formula (III), where r is0 or 1. Particularly preferably, the radical R² is,

In particular, the process according to the invention has provensuccessful for preparing the salts of 2-(2′,4′-diaminophenoxy)-ethanolfrom 2-(2′,4′-dinitrophenoxy)-ethanol, where Y^(⊖) is preferably Cl^(⊖),^(½)(SO₄)^(2⊖) or ⅓(PO₄)^(3⊖).

A process for the preparation of 1-substituted 2,4-dinitrobenzenes ofthe formula (IV) is described in a German Patent Application filed onthe same date. Other processes are known from DE-A-27 58 735, J. Chem.Soc. 1921 (119), 2076-8 and U.S. Pat. No. 2,988,571.

The hydrogenation of the 1-substituted 2,4-dinitrobenzenes according toformula (IV) is carried out in the presence of hydrogenation catalysts,which are sufficiently known to the person skilled in the art. Examplesof such catalysts include noble metal catalysts based on platinum orpalladium. It is also possible to use Raney nickel or Raney cobaltcatalysts, which can, if appropriate, be alloyed with other metals suchas molybdenum, titanium, vanadium, magnesium, iron or chromium. Thehydrogenation catalysts can be supported or unsupported.

The hydrogenation is generally carried out in the presence of a solvent.Examples of suitable solvents are branched or unbranched aliphaticalcohols, preferably isopropanol, and optionally substituted aromatichydrocarbons such as toluene or chloroaromatics. The hydrogenation isgenerally carried out at a hydrogen pressure of 0.1 to 10 MPa,preferably 0.5 to 5 MPa and at a temperature of 20 to 150° C.,preferably 40 to 120° C.

The reaction product obtained after the hydrogenation of the1-substituted 2,4-dinitrobenzenes of the formula (IV) is separated fromthe catalyst and is introduced into an aqueous solution of an acidH^(⊕)Y^(⊖), in which Y^(⊖) is the equivalent amount of a monovalent,divalent or trivalent basic acid anion.

The acid H^(⊕)Y^(⊖) is preferably hydrochloric acid, sulphuric acid orphosphoric acid, e.g, Y^(⊖) is Cl^(⊖), ^(½)(SO₄)^(2⊖) or ⅓(PO₄)^(3⊖).The acid H^(⊕)Y^(⊖) is introduced in an amount such that the molar ratioof the acid H^(⊕)Y^(⊖), to the reaction product of the hydrogenation,i.e., the 1-substituted 2,4-diamino-benzene, is at least 2:1.

It has also proven successful to add the reaction product obtained afterthe hydrogenation and separated from the catalyst to an initial chargewhich includes not only the aqueous solution of the acid H^(⊕)Y^(⊖), butalso a solvent which is miscible with the acid H^(⊕)Y^(⊖) water.Preference is given to using isopropanol as such a solvent. As a result,a further increase in the yield can be achieved. It has provensuccessful to carry out the reaction using an inert gas.

The invention provides numerous advantages. For instance, unlike theprocess in DE-A-27 58 735 discussed in the Background of the Invention)the present invention avoids the low yields obtained by this process aswell as avoids the deep violet color containing considerable amounts ofby-products and decomposition products. As such, the invention providesa valuable process for preparing an important class of compounds.

The invention is further illustrated but is not intended to be limitedby the following examples in which all parts and percentages are byweight unless otherwise specified.

EXAMPLES Example 1

A 1 l autoclave reactor was filled with 120 g of2-(2′,4′-dinitrophenoxy)ethanol, 3 g of a 1% platinum/carbon catalystwhich included 50% water, and 400 ml of isopropanol. At a hydrogenpressure of 1 MPa and a temperature of 100° C., hydrogenation wascarried out for 10 h. The system was then cooled to 20° C., and thereaction mixture was added dropwise under a nitrogen atmosphere througha filter into an initial charge of 240 g of 37% strength hydrochloricacid which had been previously flushed repeatedly with nitrogen. Theresulting suspension was heated at reflux temperature for about 30 minand then cooled to 10° C. The product obtained after filtration waswashed once with isopropanol to give 113.1 g of2-(2′,4′-diamino-phenoxy)ethanol (89.1% yield) in 98% purity. Measuringthe degrees of transmission of a 0.1% strength solution of the productin water in accordance with DIN 55945 gave, as results, T_(x)=99.4,T_(y)=98.9 and T_(z)=98.2.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A process for preparing a salt of 1-substituted2,4-diaminobenzenes of the formula (I)

wherein each R¹ is a component comprising a member selected from thegroup consisting of linear C₁-C₂₀-alkyl groups, branched C₁-C₂₀-alkylgroups, C₆-C₁₈-aryl groups, C₂-C₂₀-acyl groups, COOH groups, COOR³groups; wherein R³ is a linear or a branched C₁-C₂₀-alkyl radical, or aN(R⁴)₂ group, in which each R⁴ is hydrogen, a linear or a branchedC₁-C₂₀-alkyl radical or a C₂-C₂₀-acyl radical, and n is an integer from0 to 3; R² is a radical of the formula (II)

wherein each R⁵ is hydrogen or a C₁-C₅-alkyl radical, m is an integerfrom 1 to 12 and p is an integer from 1 to 4, or a radical of theformula (III),

wherein each r is an integer from 0 to 2 and optionally one or morecarbon atoms of the phenyl ring are replaced by N, O or S, and Y^(⊖) isan equivalent amount of a monovalent, divalent or a trivalent basic acidanion; the process comprising the steps of A) catalyticallyhydrogenating a 1-substituted 2,4-dinitrobenzenes of the formula (IV) inthe presence of a catalyst,

 wherein R¹, n and R² have the meanings given for formula (I) to form areaction product; and B) separating the reaction product obtained afterhydrogenation of 1-substituted 2,4-dinitrobenzenes of the formula (IV)from the catalyst and adding the reaction product to an aqueous solutionof an acid H^(⊕)Y^(⊖), wherein Y^(⊖) has the meaning given above.
 2. Theprocess of claim 1, wherein in the formula (I), each R¹ is a componentcomprising a member selected from the group consisting of linearC₁-C₁₀-alkyl groups, branched C₁-C₁₀-alkyl groups, C₆-C₁₂-aryl groups,C₂-C₆-acyl groups and N(R⁴)₂ groups, in which each R⁴ is hydrogen, alinear or a branched C₁-C₆-alkyl radical or a C₂-C₆-acyl radical, andindependently thereof n is an integer from 0 to
 2. 3. The process ofclaim 1, wherein in formula (I), R² is a radical of the formula (II), inwhich m is an integer from 1 to 9, R⁵ is hydrogen or methyl, and p is 1or
 2. 4. The process of claim 3, wherein m is 1, 2 or
 3. 5. The processof claim 1, wherein the radical R² in the formula (II) is —[CH₂—CH₂]—,—[CH(CH₃)—CH₂]— or —[CH₂—C(CH₃)₂—CH₂]—, in which p is
 1. 6. The processof claim 1, wherein R² is a radical of the formula (III), in which r is0 or
 1. 7. The process of claim 6, wherein the radical R² is


8. The process of claim 1, wherein the hydrogenation of the1-substituted 2,4-dinitrobenzenes of the formula (IV) is carried out inthe presence of a catalyst component comprising a member selected fromthe group consisting of noble metal catalysts based on platinum, noblemetal catalysts based on palladium, Raney nickel catalysts, and Raneycobalt catalysts.
 9. The process of claim 1, wherein the hydrogenationis carried out at a hydrogen pressure ranging from about 0.1 to about 10MPa at a temperature ranging from about 20 to about 150° C.
 10. Theprocess of claim 9, wherein the process is carried out at a hydrogenpressure ranging from about 0.5 to about 5 MPa at a temperature rangingfrom about 40 to about 120° C.
 11. The process of claim 1, wherein theacid H^(⊕)Y^(⊖) is an acid comprising a member selected from the groupconsisting of hydrochloric acid, sulphuric acid and phosphoric acid. 12.The process of claim 1, wherein the salt of 1-substituted2,4-diamino-benzenes of the formula (I) produced is the salt of2-(2′,4′-diaminophenoxy)-ethanol.